Wednesday, February 5, 2014

New paper explains how lunar tides can control climate

A paper published today in the Journal of Geophysical Research Atmospheres finds that the natural atmospheric oscillation the Southern Annual Mode [SAM] is forced by the 18.6 year lunar tidal cycle. The SAM in turn has profound effects on climate of the Southern Hemisphere, on Antarctic sea ice, precipitation in Africa, etc. and interacts with other global atmospheric and ocean oscillations. Prior papers have also demonstrated solar forcing of the SAM. The papers add to hundreds of peer-reviewed publications demonstrating both solar amplification mechanisms and lunar tidal forcing of the major atmospheric and ocean oscillations, which in turn dominate global climate.

Synoptic weather data and rainfall records are used to support previous suggestions that the decadal-scale cycle in certain climate records may be attributed to the modulation in tidal forcing related to the 18.6 year lunar nodal cycle. The Southern Annular Mode (SAM) is shown to be sensitive to tidal forcing on a daily time scale. It is subsequently shown that the late-summer SAM can be predicted by consideration of tidal potential. The seasonal response in the SAM is also reflected in sea surface temperatures. Observed behavior of the atmosphere suggests that changing tidal potential over the lower versus higher latitudinal regions plays a role. The atmospheric response as reflected in the changing SAM affects the daily rainfall variation in certain subtropical parts of southern Africa where rainfall correlates positively with the SAM. The daily rainfall response subsequently accumulates in a bi-decadal rainfall cycle, known over southern Africa as the Dyer-Tyson cycle.